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www.preene.com
GROUNDWATER CONTROL TECHNIQUES FOR
TUNNELLING AND SHAFT SINKING
Dr Martin Preene
Preene Groundwater Consult...
www.preene.com
GROUNDWATER CONTROL TECHNIQUES
Synopsis
• Background and definitions
• Groundwater control techniques:
– by...
www.preene.com
PRACTICE PROFILE
Preene Groundwater Consulting is the Professional Practice
of Dr Martin Preene and provide...
www.preene.com
GROUNDWATER CONTROL
Definition
Groundwater Control
“The process of temporarily dealing with groundwater, to...
www.preene.com
GROUNDWATER CONTROL
Additional Definitions:
Permeability = coefficient of permeability = hydraulic conducti...
www.preene.com
GROUNDWATER CONTROL
Two main philosophies of groundwater control:
• Pumping: Arrays of wells or sumps (cons...
www.preene.com
GROUNDWATER CONTROL BY PUMPING
• Typically relies on
arrays or groups of
pumped wells and/or
sumps, acting
...
www.preene.com
GROUNDWATER CONTROL BY PUMPING
Available Techniques
• Sump pumping
• Wellpoints
• Deepwells
• Ejector wells...
www.preene.com
SUMP PUMPING
Sump pumping
during construction
of a large diameter
shaft in Sherwood
Sandstone
www.preene.com
WELLPOINTS
From CIRIA Report
C515 (2000):
Groundwater Control:
Design and Practice
www.preene.com
DEEPWELLS
From CIRIA Report
C515 (2000):
Groundwater Control:
Design and Practice
www.preene.com
EJECTOR WELLS
From CIRIA Report
C515 (2000):
Groundwater Control:
Design and Practice
www.preene.com
RELIEF WELLS
www.preene.com
HORIZONTAL (HDD) WELLS
www.preene.com
• Shaft or caisson
constructed
• Perforated ‘laterals’
driven out from
shaft
• One pump (located
in the sha...
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ELECTRO-OSMOSIS
From CIRIA Report C515
(2000): Groundwater
Control: Design and
Practice
www.preene.com
ARTIFICIAL RECHARGE
www.preene.com
EXCLUSION: VERTICAL CUT-OFF WALLS
Cut-off walls penetrate
into underlying low
permeability stratum
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EXCLUSION: CUT-OFF WALLS AND PUMPED WELLS
Cut-off walls do not reach deep
impermeable stratum: dewatering
w...
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EXCLUSION: VERTICAL CUT-OFF AND HORIZONTAL BARRIERS
Cut-off walls do not reach deep
impermeable stratum:
ho...
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JOINTS AND LEAKS IN CUT-OFF WALLS
Walls installed as panels or sections
Walls installed
as line of
overlapp...
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ALTERNATIVE GEOMETRIES OF GROUNDWATER BARRIERS
www.preene.com
EXCLUSION TECHNIQUES
• Displacement barriers
– Steel sheet-piles
• Excavated barriers
– Concrete diaphragm ...
www.preene.com
STEEL SHEET-PILING
Circular sheet-
pile cofferdam
with concrete
walings
www.preene.com
CONCRETE DIAPHRAGM WALLS
Circular
concrete
diaphragm
wall
www.preene.com
CONCRETE DIAPHRAGM WALLS
Rope operated
diaphragm wall grab
Construction sequence for diaphragm walls
from W...
www.preene.com
BORED PILE WALLS
Contiguous pile wall – concrete piles installed at a spacing of more than one pile diamete...
www.preene.com
BENTONITE SLURRY WALLS
Excavation of slurry trenches can be by long
reach backhoe down to 15 to 25 m.
Deepe...
www.preene.com
BENTONITE SLURRY WALLS
Bentonite-cement slurry wall
constructed by long reach
excavator
Common European pra...
www.preene.com
GROUTING
Definition:
• Grouting is the process of controlled injection of a
fluid (grout) into the pores (i...
www.preene.com
GROUTING IN SOILS AND ROCKS
Permeation grouting
(in soils) – little or no
disturbance of
soil structure
Roc...
www.preene.com
GROUTING
• Most grouts are suspensions of particles in water (with
other additives). Cement-based grouts ar...
www.preene.com
GROUTING
Indicative grout types
For different types of soil
www.preene.com
JET GROUTING
Structure of
soils or soft
rocks is
disrupted to
create
overlapping
columns of
mixed grout
and...
www.preene.com
JET GROUTING
Jet grouting rig operating with jetting
head above ground level
Source: Keller Geotechnique
Je...
www.preene.com
ARTIFICIAL GROUND FREEZING
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ARTIFICIAL GROUND FREEZING
Artificial ground
freezing system around
a shaft
Source: British
Drilling and
Fr...
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ARTIFICIAL GROUND FREEZING (BRINE)
AGF using brine circulation Portable brine freeze plant – This freeze pl...
www.preene.com
ARTIFICIAL GROUND FREEZING (LN)
Schematic diagram of
liquid nitrogen (LN) freezing
system
On-site liquid ni...
www.preene.com
RANGE OF APPLICATION OF METHODS
Amount of
lowering of
groundwater
level
Low permeability (silts) High perme...
www.preene.com
RANGE OF APPLICATION OF METHODS
Low permeability (silts) High permeability (gravels)
From CIRIA Report
C515...
www.preene.com
SOME TUNNELLING AND SHAFT SINKING PROBLEMS
There are some interesting problems and challenges associated
wi...
www.preene.com
THE TUNNEL AS A DRAIN
• A tunnel being constructed
with an open face will act as a
drain and water will ent...
www.preene.com
THE TUNNEL AS A DRAIN
• Geometry of the groundwater flow regime can be more
complex in long section
Example...
www.preene.com
RUNNING SAND
• Running sand is often mentioned
in relation to ‘bad ground’ in
tunnelling and shaft sinking
...
www.preene.com
RUNNING SAND
s‘ = s - u
Soil shear strength
t = s’tanf’
Effective stress = total stress - pore water pressu...
www.preene.com
RUNNING SAND
Dewatering used to lower groundwater levels and
prevent running sand during shaft construction...
www.preene.com
TUNNELLING WITHOUT DEWATERING
• On many projects shafts or vertical structures may be
dewatered, but the tu...
www.preene.com
COMPRESSED AIR WORKING
1 bar air pressure
approximates to
10 m head of water
www.preene.com
COMPRESSED AIR WORKING
• Compressed air working for tunnelling was developed in the
late 19th century
• Up ...
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FULL FACE TBMS
TBM exposed
in cofferdam
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ADVANCE DEWATERING OF TUNNELS
• While shafts and tunnel portals are routinely dewatered, it is rare to
carr...
www.preene.com
ADVANCE DEWATERING OF TUNNELS
• On the Jubilee Line Extension (JLE) project in London
in the late 1990s a d...
www.preene.com
ADVANCE DEWATERING OF TUNNELS
• The Channel Tunnel Rail Link (CTRL) London Running Tunnels took this
a stag...
www.preene.com
CROSS-PASSAGE CONSTRUCTION
• Many transportation tunnels are twin bore, and
require cross-passages to be co...
www.preene.com
CROSS-PASSAGE CONSTRUCTION
• The geometry can be difficult, short drives between
tunnels, often in poorly i...
www.preene.com
CROSS-PASSAGE CONSTRUCTION
Plan view
Section
www.preene.com
CROSS-PASSAGE CONSTRUCTION
Examples of wellpoints or drains penetrating
through segmental tunnel linings
www.preene.com
CROSS-PASSAGE CONSTRUCTION
Wellpoint pump
For tunnel
cross-passage
dewatering system
www.preene.com
GROUNDWATER CONTROL TECHNIQUES FOR
TUNNELLING AND SHAFT SINKING
Dr Martin Preene
Preene Groundwater Consult...
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Groundwater Control Techniques for Tunnelling and Shaft Sinking

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Groundwater Control Techniques for Tunnelling and Shaft Sinking

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Groundwater Control Techniques for Tunnelling and Shaft Sinking

  1. 1. www.preene.com GROUNDWATER CONTROL TECHNIQUES FOR TUNNELLING AND SHAFT SINKING Dr Martin Preene Preene Groundwater Consulting May 2015
  2. 2. www.preene.com GROUNDWATER CONTROL TECHNIQUES Synopsis • Background and definitions • Groundwater control techniques: – by pumping – by exclusion • Guidelines for selecting the best technique • Some tunnelling and shaft sinking problems • A bit of dewatering design and philosophy
  3. 3. www.preene.com PRACTICE PROFILE Preene Groundwater Consulting is the Professional Practice of Dr Martin Preene and provides specialist advice and design services in the fields of dewatering, groundwater engineering and hydrogeology to clients worldwide Dr Martin Preene has more than 25 years’ experience on projects worldwide in the investigation, design, installation and operation of groundwater control and dewatering systems. He is widely published on dewatering and groundwater control and is the author of the UK industry guidance on dewatering (CIRIA Report C515 Groundwater Control Design and Practice) as well as a dewatering text book (Groundwater Lowering in Construction: A Practical Guide to Dewatering)
  4. 4. www.preene.com GROUNDWATER CONTROL Definition Groundwater Control “The process of temporarily dealing with groundwater, to allow excavations to be made in dry and stable conditions below natural groundwater level” May be known as Dewatering or Construction Dewatering or Groundwater Lowering
  5. 5. www.preene.com GROUNDWATER CONTROL Additional Definitions: Permeability = coefficient of permeability = hydraulic conductivity (units of m/s). Typically given the symbol k High to moderate permeability: Gravel, sand and gravel, sand, silty sand Porous and fractured rock Low to very low permeability: Silt, clay Unfissured and ‘tight’ rock Drawdown = amount of vertical lowering of groundwater level due to pumping (units of metres)
  6. 6. www.preene.com GROUNDWATER CONTROL Two main philosophies of groundwater control: • Pumping: Arrays of wells or sumps (construction dewatering) • Exclusion: Physical cut-off walls
  7. 7. www.preene.com GROUNDWATER CONTROL BY PUMPING • Typically relies on arrays or groups of pumped wells and/or sumps, acting together, to lower groundwater levels over a wide area • Commonly known as dewatering
  8. 8. www.preene.com GROUNDWATER CONTROL BY PUMPING Available Techniques • Sump pumping • Wellpoints • Deepwells • Ejector wells • Relief wells • Horizontal wells • Collector wells • Electro-osmosis • Artificial recharge
  9. 9. www.preene.com SUMP PUMPING Sump pumping during construction of a large diameter shaft in Sherwood Sandstone
  10. 10. www.preene.com WELLPOINTS From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  11. 11. www.preene.com DEEPWELLS From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  12. 12. www.preene.com EJECTOR WELLS From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  13. 13. www.preene.com RELIEF WELLS
  14. 14. www.preene.com HORIZONTAL (HDD) WELLS
  15. 15. www.preene.com • Shaft or caisson constructed • Perforated ‘laterals’ driven out from shaft • One pump (located in the shaft) can achieve high yields, can be much more widely spaced than conventional deepwells COLLECTOR WELLS
  16. 16. www.preene.com ELECTRO-OSMOSIS From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  17. 17. www.preene.com ARTIFICIAL RECHARGE
  18. 18. www.preene.com EXCLUSION: VERTICAL CUT-OFF WALLS Cut-off walls penetrate into underlying low permeability stratum
  19. 19. www.preene.com EXCLUSION: CUT-OFF WALLS AND PUMPED WELLS Cut-off walls do not reach deep impermeable stratum: dewatering wells are needed
  20. 20. www.preene.com EXCLUSION: VERTICAL CUT-OFF AND HORIZONTAL BARRIERS Cut-off walls do not reach deep impermeable stratum: horizontal barrier is used to exclude groundwater from base
  21. 21. www.preene.com JOINTS AND LEAKS IN CUT-OFF WALLS Walls installed as panels or sections Walls installed as line of overlapping columns Walls or barriers installed as multiple line of overlapping columns
  22. 22. www.preene.com ALTERNATIVE GEOMETRIES OF GROUNDWATER BARRIERS
  23. 23. www.preene.com EXCLUSION TECHNIQUES • Displacement barriers – Steel sheet-piles • Excavated barriers – Concrete diaphragm walls – Bored pile walls (secant pile walls and contiguous pile walls) – Bentonite slurry walls and trenches • Injected barriers – Permeation grouting – Rock grouting – Jet grouting – Mix-in-place methods • Artificial ground freezing • Compressed air (for tunnels and shafts) and full face TBMs
  24. 24. www.preene.com STEEL SHEET-PILING Circular sheet- pile cofferdam with concrete walings
  25. 25. www.preene.com CONCRETE DIAPHRAGM WALLS Circular concrete diaphragm wall
  26. 26. www.preene.com CONCRETE DIAPHRAGM WALLS Rope operated diaphragm wall grab Construction sequence for diaphragm walls from Woodward (2005): An Introduction to Geotechnical Processes Source: Bachy Soletanche Rockmill diaphragm wall cutter (hydromill or Hydrofraise) Source: Cementation Skanska
  27. 27. www.preene.com BORED PILE WALLS Contiguous pile wall – concrete piles installed at a spacing of more than one pile diameter Secant pile wall – overlapping concrete piles installed at a spacing of less than one pile diameter
  28. 28. www.preene.com BENTONITE SLURRY WALLS Excavation of slurry trenches can be by long reach backhoe down to 15 to 25 m. Deeper trenches are typically excavated by clamshell grabs or hydromills
  29. 29. www.preene.com BENTONITE SLURRY WALLS Bentonite-cement slurry wall constructed by long reach excavator Common European practice Soil-bentonite slurry wall constructed by long reach excavator Common North American practice
  30. 30. www.preene.com GROUTING Definition: • Grouting is the process of controlled injection of a fluid (grout) into the pores (in soil) or fissures (in rock) of the ground, where the grout sets and changes the properties of the in-situ material, typically by reducing permeability and increasing strength
  31. 31. www.preene.com GROUTING IN SOILS AND ROCKS Permeation grouting (in soils) – little or no disturbance of soil structure Rock grouting – little or no disturbance of rock structure
  32. 32. www.preene.com GROUTING • Most grouts are suspensions of particles in water (with other additives). Cement-based grouts are the most common type used for groundwater control • The penetration distance of grout into soil and rock is controlled by the relative sizes of the grout particles and the soil or rock openings. Distance of penetration is often very limited, unless the soil is very porous or the rock fissures are very open
  33. 33. www.preene.com GROUTING Indicative grout types For different types of soil
  34. 34. www.preene.com JET GROUTING Structure of soils or soft rocks is disrupted to create overlapping columns of mixed grout and disturbed in-situ material
  35. 35. www.preene.com JET GROUTING Jet grouting rig operating with jetting head above ground level Source: Keller Geotechnique Jet grouting systems from Woodward (2005): An Introduction to Geotechnical Processes
  36. 36. www.preene.com ARTIFICIAL GROUND FREEZING
  37. 37. www.preene.com ARTIFICIAL GROUND FREEZING Artificial ground freezing system around a shaft Source: British Drilling and Freezing Co. Ltd
  38. 38. www.preene.com ARTIFICIAL GROUND FREEZING (BRINE) AGF using brine circulation Portable brine freeze plant – This freeze plant is driven by a 180-kW electric motor. The output is 166 320 kcal/h when evaporating at −37.5°C Source: British Drilling and Freezing Co. Ltd
  39. 39. www.preene.com ARTIFICIAL GROUND FREEZING (LN) Schematic diagram of liquid nitrogen (LN) freezing system On-site liquid nitrogen (LN) storage tank receiving a LN delivery by road tanker
  40. 40. www.preene.com RANGE OF APPLICATION OF METHODS Amount of lowering of groundwater level Low permeability (silts) High permeability (gravels) From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  41. 41. www.preene.com RANGE OF APPLICATION OF METHODS Low permeability (silts) High permeability (gravels) From CIRIA Report C515 (2000): Groundwater Control: Design and Practice
  42. 42. www.preene.com SOME TUNNELLING AND SHAFT SINKING PROBLEMS There are some interesting problems and challenges associated with tunnelling and shaft sinking projects: • The tunnel as a drain • Running sand • Tunnelling without ‘dewatering’ • Advance dewatering of tunnels • Cross-passage construction
  43. 43. www.preene.com THE TUNNEL AS A DRAIN • A tunnel being constructed with an open face will act as a drain and water will enter the tunnel • If rates of groundwater inflow are manageable, and face instability is not a concern (e.g. in rock) then this can be a viable method of ‘groundwater control’ • Inflows can be reduced by grouting ahead of the tunnel
  44. 44. www.preene.com THE TUNNEL AS A DRAIN • Geometry of the groundwater flow regime can be more complex in long section Example of segmentally lined tunnel with open face shield Direction of progress Groundwater flow Groundwater level lowered above working face
  45. 45. www.preene.com RUNNING SAND • Running sand is often mentioned in relation to ‘bad ground’ in tunnelling and shaft sinking • It is not a type of material, it is a state in which a granular material can exist, when pore water pressures are high and the material strength becomes very low • Dewatering can lower pore water pressures and transform material into more stable ground Running sand in the base of a shaft
  46. 46. www.preene.com RUNNING SAND s‘ = s - u Soil shear strength t = s’tanf’ Effective stress = total stress - pore water pressure Groundwater flow Sump pumping within an underpinned shaft
  47. 47. www.preene.com RUNNING SAND Dewatering used to lower groundwater levels and prevent running sand during shaft construction in Glacial Sand deposits Groundwater flow Underpinned shaft with advance dewatering by external wells
  48. 48. www.preene.com TUNNELLING WITHOUT DEWATERING • On many projects shafts or vertical structures may be dewatered, but the tunnel itself is not dewatered directly, even where it is below groundwater level • Tunnelling can still be carried out in a ‘shirt sleeve environment’ • This is the result of a groundwater exclusion approach • This can be achieved by compressed air working or full face TBMs (EPB or slurry)
  49. 49. www.preene.com COMPRESSED AIR WORKING 1 bar air pressure approximates to 10 m head of water
  50. 50. www.preene.com COMPRESSED AIR WORKING • Compressed air working for tunnelling was developed in the late 19th century • Up until the 1980s and 1990s compressed air was used relatively widely in the UK to allow hand or mechanised excavation below groundwater level using open face shields • There are health risks associated with compressed air working (decompression sickness, bone necrosis) • Compressed air working is now largely limited to short term use such as interventions to access the front of a TBM to change cutters mid-drive or to deal with obstructions
  51. 51. www.preene.com FULL FACE TBMS TBM exposed in cofferdam
  52. 52. www.preene.com ADVANCE DEWATERING OF TUNNELS • While shafts and tunnel portals are routinely dewatered, it is rare to carry out advance dewatering for tunnel drives themselves • This may be due to lack of surface access for wells, or because tunnelling methods (e.g. TBMs) do not require it • However, even if dewatering of tunnel drives is not ‘necessary’ there can be operational and efficiency advantages from dewatering (or depressurisation) of tunnel drives: – Improved production rates – Reduced moisture content of spoil – Easier (depressurised) conditions for cross-passage construction and TBM cutter head maintenance
  53. 53. www.preene.com ADVANCE DEWATERING OF TUNNELS • On the Jubilee Line Extension (JLE) project in London in the late 1990s a de-facto advance dewatering system in the Chalk and Basal Sands was adopted when the drawdown effect of dewatered neighbouring shafts interacted • This allowed the existing TBMs to operate in open mode (rather than closed mode), thereby improving tunnel production
  54. 54. www.preene.com ADVANCE DEWATERING OF TUNNELS • The Channel Tunnel Rail Link (CTRL) London Running Tunnels took this a stage further in the early 2000s and developed a planned advance dewatering system to depressurise the Chalk and Basal Sands. • 39 wells at 22 locations, pumping up to 700 l/s • This highlighted some of the challenges of advance dewatering: – The Project Client had to purchase parcels of land on which to locate the wells – The local sewer network could not cope with the pumped dewatering flow rate, so a 3.5 km long water disposal main (up to 600 mm diameter) had to be constructed below the streets • Some of the wells were installed to water industry standards and were subsequently adopted by Thames Water
  55. 55. www.preene.com CROSS-PASSAGE CONSTRUCTION • Many transportation tunnels are twin bore, and require cross-passages to be constructed periodically along the route for access, maintenance and ventilation • Other headings or tunnel enlargements may be needed at shafts and stations • If the tunnels are constructed by full-face TBMs, then the cross-passages may be the only explicit groundwater control required for the tunnels
  56. 56. www.preene.com CROSS-PASSAGE CONSTRUCTION • The geometry can be difficult, short drives between tunnels, often in poorly investigated areas • Groundwater exclusion strategies can be attractive – grouting, artificial ground freezing • Groundwater depressurisation – radial wells – can also be used. The wells will flow naturally into the tunnel, but usually need to be pumped • Challenges relate to drilling out through tunnel lining for wells, including sub-horizontally and upwards
  57. 57. www.preene.com CROSS-PASSAGE CONSTRUCTION Plan view Section
  58. 58. www.preene.com CROSS-PASSAGE CONSTRUCTION Examples of wellpoints or drains penetrating through segmental tunnel linings
  59. 59. www.preene.com CROSS-PASSAGE CONSTRUCTION Wellpoint pump For tunnel cross-passage dewatering system
  60. 60. www.preene.com GROUNDWATER CONTROL TECHNIQUES FOR TUNNELLING AND SHAFT SINKING Dr Martin Preene Preene Groundwater Consulting May 2015

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